States of Matter and Atomic Theory

A comprehensive set of vocabulary flashcards covering matter, atomic structure, states of matter, properties, pure substances, mixtures, chemical formulas, naming conventions, and fundamental chemical laws and theories.

Matter

Anything that takes up space and has weight; the substance of which objects are made.

Atom

The basic building block of matter; smallest unit of an element; extremely small particle.

Molecule

Two or more atoms bonded together (e.g., H2O, CO2).

Ion

A charged particle (positive or negative) formed when electrons are gained or lost.

Proton

Positively charged subatomic particle located in the nucleus; ~1 atomic mass unit.

Neutron

Electrically neutral subatomic particle in the nucleus; ~1 atomic mass unit.

Electron

Negatively charged subatomic particle orbiting the nucleus; very small mass.

Nucleus

Center of the atom where protons and neutrons reside.

Atomic Number (Z)

Number of protons in the nucleus; identifies the element.

Mass Number (A)

Total number of protons and neutrons in the nucleus.

Isotope

Atoms of the same element (same Z) with different numbers of neutrons (different A).

A/Z X Notation

Isotope notation: mass number A, atomic number Z, element symbol X.

Subatomic Particles

Protons, neutrons, and electrons—the basic parts of an atom.

Electron Shell

Regions around the nucleus where electrons are located; 2 in first shell, up to 8 in subsequent shells.

Atom Size Relative to Nucleus

Nucleus is about 100,000 times smaller than the overall atom.

Avogadro’s Number

6.022 × 10^23 particles per mole; links microscopic and macroscopic.

Size of Atoms (0.1–0.5 nm)

Typical atomic/molecular size affecting interactions and energy exchange.

Solid

state with definite shape and volume; particles tightly packed and vibrating.

Liquid

State with definite volume but no definite shape; flows and takes container shape.

Gas

State with no definite shape or volume; particles move freely to fill space.

Plasma

Ionized gas with charged particles; common in stars and neon signs.

Bose–Einstein Condensate (BEC)

State near absolute zero where bosons act as a single quantum entity.

Pure Substances

Fixed composition with uniform properties; cannot be separated by physical means.

Elements

Substances consisting of one type of atom; defined by protons (Z).

Compounds

Two or more elements chemically bonded in fixed ratios; new properties.

Mixtures

Two or more substances physically combined; retain individual properties.

Homogeneous Mixtures

Uniform composition; components not visually distinguishable (solutions).

Heterogeneous Mixtures

Non-uniform composition; components visibly distinct.

Physical Properties

Observable without changing chemical identity (color, melting point, boiling point, density, hardness).

Intensive Properties

Do not depend on amount of matter (density, boiling point, color, hardness, luster).

Extensive Properties

Depend on the amount of matter (volume, mass, total energy, length).

Density

Mass per unit volume; constant for a given substance.

Melting Point

Temperature at which a solid changes to a liquid.

Boiling Point

Temperature at which a liquid boils to a gas at standard pressure.

Color

Visual property of substances (e.g., gold is yellow, copper is reddish-brown).

Hardness

Resistance to scratching; measured on a scale like Mohs.

Luster

Shininess of a metal or surface.

Flammability

Tendency to burn in the presence of oxygen.

Oxidation

Reaction with oxygen (e.g., iron rusting).

Reactivity

Tendency to undergo chemical change in response to another substance.

Toxicity

Harmful effects on biological systems.

Conservation of Mass

Mass is neither created nor destroyed in a chemical reaction.

Constant Composition (Law of Definite Proportions)

A compound always contains the same elements in the same mass ratio.

Law of Multiple Proportions

If two elements form more than one compound, the masses combine in simple whole-number ratios.

Dalton’s Atomic Theory (Postulates)

Key ideas: atoms are indivisible; atoms of an element are identical; atoms differ between elements; atoms combine in simple whole-number ratios; atoms rearrange in reactions.

Indivisible Atoms

Atoms are the fundamental, indivisible units of matter.

Identical Atoms of an Element

Atoms of a given element have the same properties.

Different Atoms of Different Elements

Atoms of different elements differ in properties and mass.

Simple Whole-Number Ratios

Atoms combine in simple whole-number ratios to form compounds.

Rearrangement in Reactions

During reactions, atoms are rearranged, not created or destroyed.

Cation

Positively charged ion; metals tend to lose electrons.

Anion

Negatively charged ion; nonmetals gain electrons.

Monoatomic Ion

Ions consisting of a single atom (e.g., Na+, Mg2+).

Polyatomic Ion

Ions made of more than one atom (e.g., MnO4−, PO4^3−).

Stock Method

Naming ions with element name and oxidation state in parentheses (e.g., Iron(II) ion).

-ide Suffix (Anions)

Used to name negatively charged monoatomic ions (e.g., sulfide, oxide).

Oxyanions

Polyatomic ions containing oxygen paired with another element; named with root + -ate/-ite.

-ate and -ite Suffixes

-ate for more oxygens, -ite for fewer oxygens.

Ionic Compound

Compound formed from a cation and anion; overall neutral.

Writing Ionic Formulas

Write cation first, then anion; balance charges to neutrality.

Acids

Compounds that release hydrogen ions (H+) in water.

Binary Acids

Acids with hydrogen and a nonmetal; name: hydro + root + ic + acid (e.g., HCl = hydrochloric acid).

Ternary Acids

Acids derived from polyatomic ions; -ite becomes -ous, -ate becomes -ic.

Covalent Compounds

Nonmetals share electrons; exist as molecules.

Binary Covalent Compounds

First element named fully; second element named with -ide; use prefixes for numbers.

Molecular Formula

Shows the actual number of atoms of each element in a molecule.

Empirical Formula

Shows the simplest whole-number ratio of elements in a compound.

Transition Metals

Metals capable of multiple oxidation states; variable ionic charges.